The core of a typical nuclear reactor may include 40,000 or more fuel rods, each containing a column of hundreds of fuel pellets. The fuel rods are arranged to generate controlled amounts of heat in specific regions of the core. Controlled heat generation is largely achieved by organizing the pellet columns in specified zones of varying lengths and uranium enrichment concentrations. Current designs call for fuel rods having as many as seven pellet zones of various specified lengths and four or more different enrichment concentrations.
Proper operation of a reactor critically depends not only on the locations of the various types of fuel rods within the core, but also on the locations of the various pellet zones of specified enrichments in the pellet column of each fuel rod. Thus, to assure requisite control of the heat generated in a reactor core such as to decrease local power peaking, to improve the power distribution throughout the bundles of fuel rods, and to provide adequate reactor shutdown margin, it is critical that the fuel rods be manufactured strictly in accordance with engineering specifications to comply with safety and regulatory requirements. Thus, each and every fuel pellet must be in a prescribed location within the pellet column according to enrichment concentration in order to achieve requisite enrichment zone lengths and zone interface positions along the column length.
As the number of enrichment zones per pellet column increases, so does the potential for manufacturing error. Thus more rigorous quality assurance measures must be instituted. Pellets of different enrichments must be maintained segregated, tracked and accounted for throughout the loading process. Each pellet enrichment zone must be precisely made up to exacting length and weight specifications and loaded into a fuel rod or cladding tube in the proper order to assure its requisite positioning in the pellet column. That is, the fuel rod must be loaded by pellet zones in accordance with predetermined engineering specifications or so-called "rod maps". Another quality assurance check is the vacant space left in the cladding tube after the last pellet zone has been loaded, which ultimately provides a plenum chamber when the tube is sealed with an end plug as the final fuel rod manufacturing step. A record must be kept of the specifications to which each rod was loaded with pellets so that the rods can be assembled into fuel bundles in proper positions.
The vast multitude of fuel pellets and the lesser but still significant number of cladding tubes to be handled and brought together, coupled with the required quality assurance checks and record keeping, makes for an involved and time consuming loading process. Consequently, the requisite fuel rod output to satisfy the needs of the nuclear power generating industry is a major concern. Manual pellet loading is too labor intensive, slow and prone to error. Automated apparatuses have been proposed and utilized to load nuclear fuel pellets into cladding tubes as evidenced by U.S. Pat. Nos. 3,735,550; 3,746,190; 3,940,908; 4,158,601; 4,235,066 and 4,243,078. However, while these apparatuses serve to automate the step of loading rows of pellets into cladding tubes, they are not equipped to fully automate the handling of the pellets and cladding tubes preparatory to the actual loading step and the handling of the cladding tubes after they have been loaded. Thus considerable human participation is required in the overall pellet loading process. The potential for production error therefore remains. Moreover, prior art pellet loading apparatuses are not equipped to automatically perform all of the quality control checks required to ensure that the cladding tubes have been loaded precisely to design specifications. Finally, the rate at which prior art apparatuses can reliably and accurately load cladding tubes with pellet columns consisting of multiple pellet zones of different enrichments and lengths is less than satisfactory.
It is accordingly an object of the present invention to provide an automated system for loading nuclear fuel rods or cladding tubes with fuel pellets.
An additional object is to provide a pellet loading system of the above-character which is capable of automatically making up multiple pellet zones of different enrichments and lengths for loading into cladding tubes.
Another object is to provide a pellet loading system of the above-character, wherein the handlings of the multiplicities of fuel pellets and cladding tubes preparatory and subsequent to loading are automated.
A further object is to provide a pellet loading system of the above-character, wherein automated quality control checks are performed at strategic points throughout the manufacturing process to assure absolute production integrity.
Yet another object is to provide a pellet loading system of the above-character, wherein data is gathered to track the movements of the particular types of fuel pellets and the individual cladding tubes through the system to create a record of what pellets were loaded into which tube.
A still further object is to provide a pellet loading system of the above-character wherein multiple cladding tubes are loaded in parallel to enable a high rate of throughput.
Other objects of the invention will in part be obvious and in part appear hereinafter.